(a) Field of the Invention
The present invention relates generally to signal distribution systems and, more particularly, to audio/visual/data signal distribution systems that distribute satellite signals typically in conjunction with standard terrestrial and/or cable signals to a plurality of individual receivers within one or more multiple dwelling units.
(b) Description of Related Art
Audio/visual/data (A-V) signal distribution systems generally rely on either a cable network or on free-space propagation for delivering A-V signals, such as television signals, to individual users or subscribers. Cable-based A-V signal distribution systems transmit one or more individual A-V signals or xe2x80x9cchannelsxe2x80x9d over wire, while free-space propagation systems transmit one or more channels over-the-air, i.e., in a wireless manner. Most large-scale cable and wireless signal distribution systems broadcast a broadband A-V signal having a plurality of individual A-V signals modulated onto one or more carrier frequencies within a discernable frequency band.
Some wireless signal distribution systems use one or more geosynchronous satellites to broadcast a broadband A-V signal to receiving units within a large geographic area while other wireless systems are land-based, using one or more land-based transmitters to broadcast to individual receiver units within smaller geographic areas or cells. A satellite A-V signal distribution system generally includes an earth station that compiles a number of individual A-V programs into a broadband signal, modulates a carrier frequency band with the broadband signal and then transmits (uplinks) the modulated signal to one or more geosynchronous satellites. The satellites amplify the received signals, shift the signals to different carrier frequency bands and transmit (downlink) the frequency shifted signals to earth for reception at individual receiving units.
The uplink and downlink broadband signals of analog satellite systems are usually divided into a plurality of transponder signals, each typically containing a single analog signal. For example, analog satellite systems operating in the so-called xe2x80x9cC-band,xe2x80x9d i.e., between 3.7 GHz and 4.2 GHz, may broadcast a plurality of transponder signals, each including a single frequency modulated analog T.V. channel. In current digital satellite systems, each transponder typically contains a number of individual channels multiplexed into a single data stream, commonly referred to as a program multiplex.
Satellite systems may also broadcast a set of transponder signals at multiple polarizations, for example, at a right-hand circular polarization (RHCP) and at a left-hand circular polarization (LHCP), within the band of carrier frequencies associated with the satellite, effectively doubling the number of channels broadcast by the system.
Satellite signal distribution systems exist for many frequency bands, including the so-called xe2x80x9cKu-band.xe2x80x9d One known Ku-band direct-to-home satellite system now in-operation uses an uplink signal having 16 RHCP transponder signals and 16 LHCP transponder signals modulated onto frequency bands between about 17.2 GHz, and about 17.7 GHz. Each of these 32 transponder signals is program-multiplexed to include digital data packets associated with e.g. about five to eight or more individual A-V programs, such as television channels, and is modulated according to a quaternary phase shift keying (QPSK) modulation scheme. The satellites associated with this system shift the uplink transponder signals to carrier frequencies ranging from approximately 12.2 GHz to approximately 12.7 GHz and transmit these frequency-shifted transponder signals back to earth for reception at each of a plurality of individual receiver units.
At the individual receiver units, a receiving antenna, typically comprising a parabolic dish antenna, is pointed in the general direction of the transmitting satellite (or other transmitting location) to receive the broadband QPSK modulated multiplex of A-V signals. Typically, such antennas include a low noise block (LNB) which amplifies, filters and shifts the incoming signal to an intermediate frequency band, such as L-band (between about 1.0 GHz and 2.0 GHz). The representative system, in particular, shifts the satellite signal to the frequency band between about 950 MHz and about 1450 MHz.
Typically, only the RHCP transponder signals or the LHCP transponder signals are mixed down to L-band, depending on which particular A-V channel a user is viewing. However, in systems having a two-channel LNB, both the RHCP and the LHCP transponder signals may be individually shifted down to a 500 MHz portion of L-band (e.g., between 950 MHz and 1450 MHz) and provided, via separate lines, to a set-top box or other integrated receiver and detector (IRD) associated with the receiver unit. At the IRD, an A-V program associated with a particular channel within one of the program-multiplexed transponder signals is decoded and provided to a television or other presentation or processing device for display and/or for processing of transmitted data, audio output, etc. However, because cable lines are inherently frequency limited, typical cables used at receiver sites (such as RG-6 and RG-59) are not capable of simultaneously transmitting all of the received satellite signals (1000 MHz) along with standard CATV signals to the IRD.
Furthermore, the receiving antennas or dishes associated with land-based or satellite-based wireless signal distribution systems are typically large and cumbersome. For example, C-band satellite dishes are generally in the range of four to five feet in diameter and, therefore, require a large amount of operating space. As a result, it can be difficult, if not practically impossible, to install a receiving antenna for each individual unit within a multiple dwelling unit (MDU), such as an apartment, condominium or townhome complex. Reception of a particular satellite signal is made even more difficult in MDUs when, as is generally the case, some of the individual dwelling units therein do not have any walls or outside exposure facing the direction in which the receiving antenna must be pointed, or these dwelling units are shadowed by surrounding buildings or other obstructions.
In the past, these disadvantages have been overcome by placing one or more receiving antennas on, for example, the roof of an MDU and then running cable to each of the individual dwelling units. For example, a system for redistributing a single, off-air signal to multiple buildings in a small geographic area is disclosed in Japanese Patent Document No. 56-47183. However, common L-band multi-user distribution solutions typically used to support single dish antenna systems are fraught with installation and maintenance problems. For example, significant roll-off or degradation of the television signals may occur in cable systems due to the poor high frequency propagation properties of standard cable lines especially at and above L-band. Broadcasting a received broadband A-V signal over an existing cable network at lower carrier frequencies may prevent the use of that network for other A-V signals, such as standard cable, CATV, UHF and VHF television signals, or may require that the some of the broadband signals or existing cable signals be eliminated due to the bandwidth restrictions of the cable network.
One system proposed by the European Telecommunications Standards Institute (ETSI) in the area of Satellite Master Antenna Television (SMATV) receives a QPSK modulated satellite television signal (which may be combined with terrestrial TV signals) and remodulates this signal according to a 64 quadrature amplitude modulation (64-QAM) technique. The SMATV system then sends this remodulated signal out over cable to one or more adjacent buildings. Likewise, U.S. Pat. No. 5,173,775 discloses a system that remodulates data portions of a satellite television signal from one modulation scheme to another, such as from FM to AM, for retransmission to subscribers. However, these systems do not specifically demonstrate how to propagate remodulated satellite signals and existing cable or terrestrial signals on the same cable line or other transmission channel in an efficient manner or demonstrate how to remodulate and broadcast a large number of transponder signals associated with one or more satellites over the same cable line or other transmission channel to one or more adjacent buildings.
The above-identified parent application discloses a signal redistribution system that transmodulates each of, for example, 32 received satellite transponder signals into a different modulation scheme and transmits each of these transmodulated signals, along with standard terrestrial signals, to each of a set of receivers within an MDU. The transmodulator disclosed in this application includes a separate channel having a satellite signal demodulator coupled to a signal remodulator for each of the received satellite transponder signals. As a result, this transmodulator unit tends to be expensive, especially when used in an MDU which includes fewer satellite signal receivers or subscribers than there are channels in the transmodulator unit, i.e., in MDUs that will never need all of the channels provided by the transmodulator unit.
The present invention relates to a low cost system and method for distributing a set of program multiplexed A-V signals and, possibly, existing terrestrial signals, to a multiplicity of receiver units within one or more MDUs using an MDU cable network or other transmission channel. According to one aspect of the present invention, a receiving antenna receives a broadband signal from, for example, a satellite or a land-based transmitter. A transmodulator transmodulates selected portions of the broadband signal into a transmodulated signal having a bandwidth that is smaller than that of the received broadband signal and transmits this transmodulated signal, typically along with standard terrestrial signals, over a communication channel, such as a cable or a wireless network, to a number of individual receiver units within an MDU. The receiver units demodulate the received transmodulated signal and provide user-specified channels to processing or display units, e.g., video displays, television sets, audio systems, computers, etc. The receiver units also send requests for user-selected channels to the transmodulator which uses these requests to select Which of the portions of the broadband signal will be transmodulated.
According to another aspect of the present invention, a signal distribution system adapted to receive a composite signal having a multiplicity of transponder signals therein includes a transmodulator that transmodulates a selected one of the transponder signals from a first modulation scheme to a second modulation scheme to produce a transmodulated signal and a transmitter that transmits the transmodulated signal over a communication channel to a plurality of individual receivers. A receiver receives a request signal from each of the plurality of individual receivers and a controller selects the selected transponder signal in response to the request signals.
According to another aspect of the present invention, a signal distribution system for distributing a composite signal having a plurality of individual program multiplex signals therein over a communication channel to a number of individual receivers includes a main receiver that receives the composite signal and a multiplicity of transmodulator channels coupled to the main receiver. Each of the multiplicity of transmodulator channels, preferably numbering less than the number of individual program multiplex signals, transmodulates a different one of the plurality of individual program multiplex signals from a first modulation scheme to a second modulation scheme to produce one of a multiplicity of transmodulated signals. A combiner combines the multiplicity of transmodulated signals at different carrier frequency bands to produce a combined signal and a transmitter transmits the combined signal over the communication channel to the individual receivers. The signal distribution system also includes a request receiver that receives a request signal from each of the individual receivers and a controller coupled to the request receiver that controls which of the plurality of individual program multiplex signals each of the multiplicity of transmodulator channels is to transmodulate.
Moreover, the signal distribution system generates an information signal, known as side data, which may include channel set-up information, frequency index set-up information, etc. This information signal is used by the receiver to select a requested signal from the plurality of individual program multiplex signals.
The signal distribution system may include a second receiver adapted to receive a terrestrial signal while the combiner may combine the multiplicity of transmodulated signals with the terrestrial signal to produce the combined signal. Furthermore, a reception device coupled to the communication channel at one of the individual receivers may include a receiver that receives the combined signal, a demodulator that demodulates a portion of the received combined signal and an individual transmitter that transmits one of the request signals to the transmodulator indicating one of the plurality of program multiplex signals to be transmodulated. If desired, the transmodulator channels may transmodulate between a quadrature phase shift keying (QPSK) modulation scheme and a quadrature amplitude modulation (QAM) scheme, such as a 128-QAM scheme.
According to a still further aspect of the present invention, a method of distributing a subset of a plurality of individual signals associated with a composite signal to multiple individual receivers includes the steps of receiving the composite signal, receiving a request signal from each of the individual receivers and choosing the subset of the plurality of the individual signals to be distributed based on the received request signals. Each of the subset of the plurality of the individual signals is transmodulated from a first modulation scheme to a second modulation scheme and is transmitted over a communication channel to the individual receivers.